The Antennapedia Complex (ANT-C) of Drosophila is a cluster of homoeotic genes which controls segmental determination during development. These genes are putative "selector switches" providing a useful model system for studying the control of differentiation pathways. Mutations in ANT-C genes cause, for example, part of the head to develop as thorax, resulting in the replacement of antennae with legs. Genetic and developmental analyses have established some of the tissues and times during development when the ANT-C genes exert their effects. The proposed study will investigate the molecular basis for the effects of ANT-C genes using cloned DNA sequences. Phage carrying inserts of ANT-C DNA will be selected from complete libraries of Drosophila DNA using the chromosome "walking" procedure. Four different DNA clones containing sequences located near the ANT-C are already available. These provide four possible starting points for isolating a series of overlapping clones leading to the Complex. The ANT-C DNA clones will initially permit several types of analysis: 1) The physical map of the DNA will be aligned with the genetic map. The many available chromosome rearrangements, with known ANT-C genetic sites as breakpoints, will be used to map complementation groups onto the physical map. 2) RNA and/or protein products of ANT-C genes will be identified using DNA-RNA filter hybridization, hybrid-selected in vitro translation, and amphibian oocyte-injection of cloned DNA. 3) DNA organization in selected mutants will be compared to wild type DNA to correlate visible phenotypes with changes in particular DNA sequences. 4) Alterations in the RNA or protein products of ANT-C genes, or in the time or place or their expression, will be explored in selected mutants. 5) The cloned DNA sequences will make possible the sensitive filter-binding assay for DNA-binding proteins, which will be analyzed comparitively in normal and mutant flies.